Replace suppressors with a clone of the original design. Negative rail diode and glitch resistor can't hurt either. Soft key is a must. You can try retuning the inputs, I think some other devices could be difficult to employ. Most SB-220 amps have pretty good input tuning but sometimes the caps drift or go bad. I can rebuild your tune capacitor if it has removable plates. SOme do some don't.

You can try retuning the inputs, I think some other devices could be difficult to employ.

Thanks Lou. I was thinking of a WD7S TU6 board for the input matching; that is if I have problems adjusting the slugs or getting into other binds on the original input circuit. Hopefully it will gooff as planned and work as intended.

Of course it is your amplifier and you can do as you wish. However I become a bitnervous when someone is going to make wholesale changes to a piece of gear and asks advice (which usually means that the questioner is unsure).First off the input impedance of a 3-500Z is 115 Ohms and two in parallel will be about 56 Ohms. So a simple pi network with 50 Ohms in and out should work pretty well(such as the WD7S circuit) You could modify the circuit a bit by adding a padder (ortrimmer) to the output side so to fine tune a bit. With the WD7S you have all those relays which might be a source of trouble and a simple band switch is less complicated.My advice is don't make a lot a changes at one time, because if you have problems youwill have difficulty tracing the root cause to the correct "mod".Good Luck Allen

Of course it is your amplifier and you can do as you wish. However I become a bitnervous when someone is going to make wholesale changes to a piece of gear and asks advice (which usually means that the questioner is unsure).Good Luck Allen

Hi Allen... I've been building gear since I was a teen, about 50 years ago. I may be confident about what I am doing, but it doesn't hurt to ask regardless. Sometimes we overlook the obvious; so playing dumb is often the safestroute

Well since no one mentioned replacement parts then I will. Harbach Electronics has a few replacement parts for the 220 including the soft-key mod that Lou mentioned and is well worth it. I would also recommend the relay even if you bought it for a spare (they do wear out). As for your Tune cap RF parts offers a direct replacement for this cap a little pricey RFP part number 73-180-35/26-131 @ $59.95 ea. I used one from Ameritron on mine but had to cut the front mounting tab down to make it fit right and it was part # 282-2112-1 @$36.52 otherwise it works just fine.

The interface for the key line is high on the list. I have to open the amp and see how bad thetuning cap is. If I can remove the plates and polish them smooth, I may go that route. Therea few on eBay from parted out SB-220s that I have been watching.This amp has never seen heavy use by myself or the previous owner; but I suspect the bandswitchand tuning cap will need some intervention due to my carelessness while chasing a fewDX stations.

The interface for the key line is high on the list. I have to open the amp and see how bad thetuning cap is. If I can remove the plates and polish them smooth, I may go that route. Therea few on eBay from parted out SB-220s that I have been watching.This amp has never seen heavy use by myself or the previous owner; but I suspect the bandswitchand tuning cap will need some intervention due to my carelessness while chasing a fewDX stations.

Pete

Pete if the band switch is bad Harbach has a replacement. The 220 I have was a freebie that was sitting outside under a carport with a blanket over it in the Hilo Rain Forest so you can imagine what it looked like. I did a complete rebuild on it. Stripping it down to a bare chassis and starting over. It already had the Harbach filter caps, soft start, and fan it also had a Peter Dahl filament transformer. But the Tune cap was pitted beyond repair and the Plate choke was bad so I home brewed one. I added the Harbach Rectifier/Metering board, grounded the grids directly added a glitch resistor and did a complete paint job and made decals for the face plate I painted it a Stainless Steel silver. I also added a stand-by switch and a Transmit LED it already had a home brew 12V keying circuit that works very well. It still has the original Eimac 3-500z's and they still have full output in fact it gained 200-300 Watts out with the grids directly grounded. I also made new Parasitic Suppressors just like the original ones. I took me a couple of months to complete but I am very happy with the results it has been a workhorse since.

Replace suppressors with a clone of the original design. Negative rail diode and glitch resistor can't hurt either. Soft key is a must. You can try retuning the inputs, I think some other devices could be difficult to employ. Most SB-220 amps have pretty good input tuning but sometimes the caps drift or go bad. I can rebuild your tune capacitor if it has removable plates. SOme do some don't.

Old thread, I know, but.............. Like Pete, K1ZJH, I recently purchased a pretty nice SB-220 without tubes. I have some spare 3-400Zs and some 3-500ZGs.My first thought was to just clean it up a bit and fix what 'might' be wrong. I rewired it for 110V (to check it out) and brought it up with a Variac. Seemed to be ok. It will be run on 220V.

However, the more I looked, the more issues I found, so since I enjoy (no, LOVE) building stuff, I decided to 'unbuild' it. The previous builder made a mess of the wiring, but that's OK. This is not my first amp. Retired, and have time.

I just wanted to thank the contributors of this topic! I've read and reread about everything amp related and learn something every day.W1QJ, I read your comment about checking the parasitic anode resistors. Sure enough, one was open.I've purchased some 47 ohm, 2 watt, Ohmite 'OY' resistors as suggested by W8JI.

I've already purchased and built the Harbach:Cap board (had my own caps)Rectifier board (does away with the Zener)Soft StartSoft key (I had already made my own, but it was not really what I wanted)

I'm not going to do a bunch of 'mods' to it, other than grounding the grids, maybe a glitch resistor.

I'm also building a LK-500, dedicated 6 Meter amp in concert with the Heathkit. I have a large supply of parts I've been acquiring for 20 years for the 6 Meter amp. I also have a machine shop, so I can make about anything. I already have a LARGE legal limit amp for 6M, but I cannot use it in my home, due to sheer physical size!I'm open to suggestions, and will be here asking questions of the 'brain trust'.

You'll want to take a close look at the tube sockets to verify the contacts are ingood shape. If overheated, the tensioners can relax. Note this overheated socketwith a good grid contact on the left, and an overheated filament contact on the right:Note that the overheated contacts don't close completely.

When hard-grounding grids, you want short & wide conductors for lowest XL.This is how I did it in my SB-220:Hardware is #4-40.

In the PA compartment sheetmetal, I had some screw holes with pulled-out threads.I installed self-clinching (PEM™) nuts and replaced all the #6 sheetmetal screws w/ #6-32 machine screws:Since they're all near the edge of the panel, I used locking pliers to squeeze them into place.A couple of scraps of steel (or flat washers) prevents marring the aluminum panels.

For a 'glitch' resistor, I used a 10Ω/20W wirewound (Ohmite B20J10RE) in place of RFC2:

David K5DBX found that adding a shroud to the fan reduces noise and increases airflow:A couple of 1-1/2" wide strips of soft aluminum (top AND bottom) gets it done.They're secured at the ends by the existing PA compartment hardware.I added a bead of silicone adhesive in the middle of the top piece.This is worthwhile, especially if you use the aftermarket fan motor (Dayton #4M070) fromGrainger. A well-known reseller offers them for twice the cost.

The OEM open-frame relay is S-L-O-W and unreliable. It's best replaced with FAST vacuum & reed relaysthat have hermetically sealed contacts. Jim W7RY devised a driver circuit that also gives youelectronically regulated and switched bias. He sells on ebay as user 'radioamplifiers'. More infois on his QRZ bio: http://www.qrz.com/db/w7ry. When you make your purchase, he emailscomplete documentation and a link to the BOM on Mouser's website.He suggests a source for the vacuum relay (Max Gain Systems) and can supply a suitable reed relay.

Hi Bryan, thank you for the reply. I've already acquired all the parts I'll need for the SB-220 and the LK-500 6 Meter amp.One question....... Why did you form the tube sockets up, to strap them to ground? Never seen that before. Seen some strange wiring on YouTube, by 11 Meter 'builders' of the SB-220.

A buddy of mine had a copper roof put over his poolside outdoor kitchen. I've got several lifetimes worth of copper flashing and also brass in my stockpile.I'm never going to do QSK with the Heathkit, so I just ordered a stock replacement. The original builder made a mess around the filament choke/relay area. I spent a couple of hours today 'unbuilding' all the sub assemblies. luckily, the builder used the 'stick a wire in a hole and solder' method. No wrapping, anywhere.

Hi Bryan, thank you for the reply. I've already acquired all the parts I'll need for the SB-220 and the LK-500 6 Meter amp.One question....... Why did you form the tube sockets up, to strap them to ground? Never seen that before. Seen some strange wiring on YouTube, by 11 Meter 'builders' of the SB-220.

A buddy of mine had a copper roof put over his poolside outdoor kitchen. I've got several lifetimes worth of copper flashing and also brass in my stockpile.I'm never going to do QSK with the Heathkit, so I just ordered a stock replacement. The original builder made a mess around the filament choke/relay area. I spent a couple of hours today 'unbuilding' all the sub assemblies. luckily, the builder used the 'stick a wire in a hole and solder' method. No wrapping, anywhere.

ronN4UE

Hi Ron,

The reason for bending the tube socket terminals up is to minimize the distance between the tube's grid pins and chassis, and thereby minimize the series reactance. I used soft copper strip that was left over from another project.

My main reasons for changing to FAST & sealed vacuum & reed relays is not QSK. It's mostly about reliability and not hot-switching. Sealed relay contacts don't oxidize. Faster switching means there's zero chance of the amplifier switching lagging RF coming from the rig. QSK, dead-quiet operation, and electronic bias regulation & switching are only bonuses. LOTS of hams have converted to vacuum relays. Some newer amplifiers come with it. My total one-time cost was about $100. Rebuilding your SB220 would be a great opportunity to do the same.

Rich, I ended up doing a full blown rebuild which included several major changes. It is no longer in anyway related to a SB-220. Added full WARC and 160 meter coverage, full QSK switching, etc. My amp was abused for many years, and it did not bother me to tear into her and give her a new chance at a new life... the original 3-500Z tubes are still clunking along at rated power.

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